Telephone system



May 112, 1936. J. WICKS TELEPHONE SYSTEM 7 Shees-Sheet 1 Filed Nov. 7, 1934 mwzixw Ema 2 INVENTOR JOHN WICKS May 11 9 .2. WICKS fi fi TELEPHONE SYSTEM Filed Nov. '7, 1934 'T Sheets-Sheet 55% F n a? 9 T0 S Li! 7 r 8 fbkllo PART i1 ma LINE RLSEJHR.

y J. wlcKs 2,040,637

TELEPHONE SYSTEM Filed Nov. 7, 1934 7 SheeQs-Sheet 5 $16.3 PARTZ 'IRI T D SIGNAI: ELE PREP OUT REPEAT INC.- REPT II-l H l4 4 s10 IQZ INC.-

SERIES DI SCrSUPY.

REPT.

INVENTOR JOHN WICKS ATTY.

\ May 12, 1936. J w cKs 2,040,637

TELEPHONE SYSTEM Filed Nov. 7, 1954 7 Sheets-Sheet 6 PART B III- n:

DISC:

SUPY.

LINE RLSE INVENTOR JOHN WICKS ATTY.

ay 12, as. J. WICKS ,MQGW

TELEPHONE SYSTEM Filed Nov. 7, 19 54 7 Sheet-Sheet 7 B Fae T 2 B m TLI ELECTRO- POLARIZED OUTGO: 3 5 SERIES SUPN. REPEAT INVENTOR JOHN I ICKS Patented May 12, 1936 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Application November 7, 1934, Serial No. 751,805

22 Claims.

The present invention relates to telephone systems in general, but is concerned more particularly with telephone systems in which automatic switches are employed in setting up connections. The broad general object of the invention may be stated to be the provision of new and improved controlling or dialling arrangements for use in a telephone system wherein automatic switching apparatus is controlled over an inter-exchange trunk line or talking circuit.

General description It has long been recognized that the satisfactory controlling of the various functions peculiar to the operation and control ofautomatic switches over inter-exchange trunk lines is a special problem apart from the problem of controlling the automatic switching apparatus in an exchange over subscribers lines local to such exchange. Inter-exchange trunk lines as referred to herein shoud not be confused with inter-ofiice trunk lines used in multi-oflice telephone systems to interconnect the various ofi'ices into which an exchange may be divided. The inter-exchange trunk lines referred to herein are those which connect the exchange of one city or village with the exchange of another city or village, which exchanges may therefore be many miles apart.

A trunk line that interconnects two exchanges separated by a considerable distance represents a sizeable financial outlay, as is well known. It has long been a practice, therefore, to economize as much as possible in the use of the conductors interconnecting two exchanges, one widely used measure of economy involving the use of a socalled phantom circuit by means of which a third talking circuit is obtained by the proper association of two physical circuits. In addition, the return on the investment has been increased substantially in many cases by using the conductors of the physical circuits separately, as single conductor telegraph lines or other lines over which telegraphic or similar signals are to be transmitted. Telephone lines so arranged are "sometimes referred to as composited lines, and the conductors leading therefrom over which the telegraphic impulses pass are referred to as the composite legs.

With the foregoing explanation in mind, it will readily be understood that the usual loop impulsing over the talking conductors of a trunk line, as employed locally in automatic exchanges, is

not suitable for use over a talking circuit extending by way of trunk line conductors from one exchange to another exchange located some distance away. In the present invention, the problem presented has been attacked along the line of providing suitable impulse transmitting and receiving equipment at either end of an interexchange trunk line or talking circuit for transmitting switch controlling and other necessary impulses as impulses of alternating current which pass over a talking circuit in the same manner as the impulses of voice current pass over the talking circuit during conversation.

One feature of the system disclosed herein is that the automatic switching apparatus in the distant exchange is made ready for operation responsive to a seizing impulse transmitted over the talking circuit when the trunk line is seized; the series of setting impulses (the impulses which bring about the desired positioning of the automatic switches) are transmitted as series of impulses of alternating current; the supervisory signals, which are necessary to indicate the removal of the receiver of the called line and the subsequent replacement of the receiver on the called line after conversation, are controlled by a single impulse of alternating current transmitted from the called exchange back over the inter-exchange talking circuit to the calling exchange when the receiver is removed and another single impulse of alternating current when the receiver is subsequently replaced; and the release of the automatic switches in the called exchange is brought about responsive to the prolonged impulse of alternating current transmitted over the talking circuit from the calling exchange to the called exchange.

When such a system of controlling the setting up, supervision, and release of automatic connections is employed, a special problem which arises is the one of preventing the operation of the responsive devices in either the called exchange or the calling exchange responsive to voice currents during conversation, and to other currents of a transitory nature; a false operation of one of the receiving signal devices would often occur and result in a false or misleading operation of the supervisory apparatus or even possibly in a premature release of the connection if special provisions were not made to forestall this.

It has also been found that the presence or absence of voice-current repeaters in a talking circuit between two exchanges, being determined generally according to the length or transmission qualities of the circuit, must be taken into consideration, for example in the selection of a frequency of alternating current to be used in the transmission of the necessary impulses.

It has been determined by experimentation that 60-cycle alternating current impulses may be used satisfactorily over either physical or phantom inter-exchange circuits provided the physical circuits are not composited for telegraph or similar use, in which case l20-cycle impulses are much more satisfactory.

When voice-current repeaters are included in the inter-exchange circuits, the frequency and voltage limitations of the voice-current repeaters commonly used are such that a higher freproblem is met by transmitting a carrier current of a frequency (IOOO-cycles for example) well within the voice range and by modulating this carrier current by means of a lower frequency (GO-cycles for example), and by arranging the signal receiving apparatus so that it will respond only to a current at the carrier frequency modulated by the determined modulating frequency. The receiving arrangement is such that it will not respond to the two frequencies when one is merely superimposed on the other, but the carrier frequency must'be actually modulated by the lower frequency current, which condition does not obtain during conversation, as will be understood. The arrangements of the receiving apparatus have been devised for responding to the carrier current when received, in impulses for switch setting purposes, and to respond selectively to the carrier current when modulated for signal purposes. In one arrangement, a combination of relays is employed which, by virtue of their operating and releasing characteristics, will respond one way when the carrier current is being received in impulses corresponding to the frequency of impulses used to position the automatic switches, and will respond in another way when carrier current modulated at the signal frequency is received. The other arrangement which has been devised for separating the signal impulses from the switch setting impulses makes use of a receiving circuit tuned to the modulating signalling current. This tuned circuit includes a signal relay which is not affected by voice currents during conversation and which is not affected by the switch-setting impulses, but which responds reliably each time the carrier current modulated at the signal frequency is received.

At this point it may be mentioned that the salient features of the invention disclosed herein, although shown and described in connection with a telephone system in which the setting of the switches in a distant exchange are controlled by calling subscribers in the originating exchange, are applicable to systems in which inter-exchange calls are completed under the control of a switchboard operator who is provided with means for controlling the positioning of the automatic switches in a distant exchange.

The foregoing objects and features of the invention, together with other objects and features not specifically mentioned, will become more apparent upon a further perusal of the specification.

Description of drawings Referring now to the accompanying drawings comprising Figs. 1 to 4, they show by means of the usual circuit diagrams a suflicient amount of the apparatus involved in a system embodying the features of the invention to enable the invention to be understood.

Fig. 1 is an inter-exchange trunking diagram showing how calls may be completed between three interconnected exchanges, A, B, and C.

Fig. 2 shows the circuit equipment associated with one end of an inter-exchange trunk line or talking circuit on which no voice-current repeaters are used, being adaptable for -cyc1e operation (used when the trunk line is not composited) and 120-cycle operation (used when the trunk line is composited) Fig. 3 shows the equipment associated with one end of an inter-exchange trunk line supplied with a voice-current repeater. In Fig. 3, the apparatus for responding selectively to the signal impulses includes a group of relays which respond selectively by virtue of their operating and release characteristics.

Fig. 4 shows a modification of the arrangement of Fig. 3, wherein the incoming-signal relay is included in a circuit tuned to the signal frequency.

Trunking arrangement Referring now particularly to Fig. 1, the exchanges A and B are assumed to be located sufliciently far from each other that a voice-current repeater station is required, while exchange B is located somewhat nearer to exchange C, so that the transmission qualities of the trunk lines between exchanges B and C are such that voice current repeaters are not required. Exchange B k is the tandem switching point as regards exchanges A and C, so that all calls from either of the outlying exchanges to the other passes through exchange B.

The group of trunk lines or talking circuits interconnecting exchanges A and B is represented by the trunk line or talking circuit 'I'Ll, extending from the impulse repeater IRI in exchange A to impulse repeater 1R2 in exchange B, by way of a repeater station, while the group of trunk lines or talking circuits interconnecting exchanges B and C is represented by the trunk lines or talking circuit TL2, extending from impulse repeater IRS in exchange B to impulse repeater ml in exchange C. It will be understood, of course, that a sufficient number of trunk lines in either interexchange group is provided to meet the traffic requirements. Each of these trunk lines is equipped for two-way telephonic operation; that is, each of the impulse repeaters IRI to LR4 is a two-way repeater. The trunk line TLI, it will be noted, passes through the voice-current repeater VCR in the repeater station. This voicecurrent repeater is assumed to be of the usual construction, wherein a vacuum-tube or similar apparatus is employed to restore attenuated voice currents to satisfactory values.

Each of the exchanges A, B, and C is assumed to be serving at present a few hundred lines. Therefore, a local connection from one subscribers line to another passes through a hundreds selector and a connector. In exchange A, one substation, 88!, is shown associated with a line terminating at the exchange in the line switch LSI. The lineswitch LSI has access to a group of hundreds selectors, of which the selector S2 is one. The selector S2 has access to a number of groups of connectors, the connector CI of the second group being indicated, as is the connector C2 in the third group. The interexchange trunk lines such as the trunk line TLI are reached through the tenth level of the selectors such as S2, by way of the impulse repeaters such as IRI. Each of the trunk lines, such as 'ILl, has an incoming selector, such as SI, associated therewith through the impulse repeater, such as IRI.

The arrangement in exchange B is similar to that described in exchange A, local substations SS2 and SS3 being shown in association with lines terminating respectively in the line switches LS2 and LS3. The line switches have common access to a group of selectors, such as the selector S3, and the selectors have access through their various levels to groups of connectors, such as the connectors C3 and C4, representing the thirdand second-level groups, respectively. The connector C3 has access to the line'of substation SS3,

and the connector C4 has access to the line of substation SS2.

Incoming selector S4 is individual to the trunk line 'I'Ll interconnecting exchanges A and B, while the incoming selector S5 is individual to the trunk line TL2, interconnecting the exchanges B and C.

The trunk lines extending to exchange A are reached by way of the tenth level of the selectors, while the trunk lines extending from exchange B to exchange C are reached by way of the ninth level of the selectors.

In exchange C, selector S6, accessible to the line switch LS4 of the local substation SS4, is representative of the group of local selectors,

while the selector S1, individual to the trunk line TL2, represents the group of incoming selectors. The connectors C5 and CB represent the third and hundreds groups, respectively, the connector 05 having access to the line of substation SS4. Although the above explained trunking arrangements follow established practice, explanation will be given at this point to facilitate a ready understanding of circuit operations to be later described.

Local callsz'n exchange B The way in which local connections are completed in exchange B will first be explained. For this purpose it will be assumed that the subscriber at substation SS2 desires to obtain conne'ction with the subscriber at substation SS3. For this purpose, the subscriber at substation SS2 removes his receiver, whereupon the lineswitch LS2 operates in the well-known manner to select an idle selector, the selector S3, for example. The selector S3 is thereupon prepared for operation, and it responds to the first digit in the desired number (the digit 3 in this case) to select an idle trunk line extending from the third level of its bank contacts, the trunk line extending to the connector C3, for example.

Upon seizure, the connector C3 is prepared for operation in the usual manner, and it responds to the two'final digits in the number (the digits 2 and O, for example) to extend the connection to the desired line, the line of substation SS3.

The established connection is released in the usual manner when the subscriber at substation SS2 replaces his receiver.

Calls from exchange B to exchange A Asume now that the subscriber at substation SS2, exchange B, desires to converse with the subscriber at SSI, exchange A. Under this condition, the subscriber at substation SS2 removes his receiver and dials the listed number of the subscriber at substation SSI, preceded by the digit 0, assigned to exchange A when called from .exchange B. Assuming that the selector S3 is the one seized by the lineswitch LS2 when the receiver is removed at substation SS2, this selector responds to the digit 0 by selecting an idle trunk line extending from the tenth level of its bank contacts, the trunk line extending by way of the impulse repeater 1R2 to the inter-exchange trunk line TLI, for example. When this trunk line is seized, the impulse repeaters 1R2 and IRI are prepared for operation, and, through the respcnse of the repeater 1R2, the incoming selector SI in exchange A is prepared for operation.

When the first digit in the listed number of the subscriber at substation SSI is now called, the selector SI responds by selecting an idle trunk line extending to a connector, such as the connector C2, having access to the line of substation SSE. The connector C2 may then respond to the two final digits of the number and extend the connection to the line of substation SSi.

The established connection is released when the calling subscriber at substation SS2 replaces his receiver.

Calls from exchange A to exchange B When a subscriber of exchange A desires to establish connection with the line of a subscriber of exchange B, the substations SSI and SS2 being assumed to be the ones involved, the connection is extended by way of the line switch LSI to a selector such as S2, and may be further extended by way of the tenth 1eve1 of the selector S2 and the impulse repeater IRI to the inter-exchange trunk line 'I'Ll, whence it extends by way of the impulse repeater 1R2 and the voice-current repeater VCR to the incoming selector S4.

final digits in the number to complete the connection.

Inter-exchange calls between exchanges B and C Inter-exchange calls may be completed between subscribers in exchange B and subscribers f" in exchange C in a manner similar to that described. For example, a connection set up from the line of substation SS2 of exchange B to the line of substation SS4 in exchange C includes the line switch LS2, and may include the selector I S3, operated to the ninth level, the impulse repeater 1R3, trunk line TL2, impulse repeater IRA. incoming selector S! and the connector C5. To complete this connection, the listed number of the subscriber at substation SS4 is dialled, preceded by the dlgit 9.

F Aninter-exchange call from the line of substation SS4, exchange C, to the line of substation SS3, exchange B, includes the line switch LS4, and may include the selector S6, operated to the tenth level, the repeaters IE4 and IE3 between which the trunk line TL2 extends, the incoming selector S5, and the connector C3. 'To complete this connection, the subscriber at substation SS4 dials the listed number of the sub 'scriber at substation SS3, preceded by the digit 0. Tandem calls between exchanges A and C A call from exchange A to exchange C is switched through exchange B, and it may be set up in a manner now to be described: In case the calling subscriber is the one at substation SSI and the called subscriber is the one at substation SS4, the connection includes the line switch LSI, and may include the local selector S2, operated to the tenth level, the repeaters ml and IE2, interconnected by the trunk line 'ILl the incoming selector S4, operated to its ninth level, impulse repeaters IE3 and IR4, interconnected by the trunk line TL2, and the incoming selector S1, as well as the connector C5. In order to establish this connection, the subscriber at substation SSI dials the listed local number of the line of the subscriber at substation SS4, preceded by the digit 0, indicating the exchange C, and the digit 9, indicating the exchange B.

Assume now that the subscriber at substation SS4 desires to converse with the subscriber at substation SSI, the established connection must be trunked through the exchange B to the exchange A. The connection includes the line switch LS4 and may include the local selector S6, the repeaters IR4 and 1R3, interconnected by the trunk line TL2, the incoming selector S5, the repeaters IE2 and IRI, interconnected by the trunk line TM, and the incoming selector Si, as well as the connector C2. To establish this connection, the subscriber at substation S4 dials the local listed number of the line of substation SSI, preceded by the digit 0, indicating the exchange B, and the further digit 0, indicating the exchange A.

Detailed description The system having been described with relation to the trunking diagram given in Fig, 1, further consideration will now be given to the circuit drawings, Figs. 2, 3, and 4. These drawings, of

course, are to be considered in connection with the trunking diagram of Fig. 1; similar parts appearing in the circuit drawings have the same reference characters applied as have the corresponding parts in Fig. 1.

Fig, 2 illustrates the impulse repeater IE3 which is located in exchange B and associated with one end of the trunk line TL2 extending between exchanges B and C. Since the trunk line TL2, according to the previous assumption, is not of suificient length or of sufficient voiceattenuating characteristics to require the use of a voice-current repeater, a relatively simple impulse and signal circuit can be used betweenthe impulse repeaters IE3 and IE3. Since the repeater IR4 may be identical in circuit arrangement with the repeater 1R3, illustrated in Fig. 2, the repeater IR4 is not illustrated in detail. The equipment shown in the upper right-hand corner of Fig. 2, part 2, and arranged to be connected up alternatively, as indicated by the dotted jumper connections, is to be used in place of the impulse repeating relay 226 when 120-cycle signalling current, in place of 60-cycle signalling current, is used on account of the associated talking circuit including a composited line.

Call from SS2, exchange B to SS4, exchange The detailed description will include first a description of Fig. 2, with reference to the trunking diagram shown in Fig. 1. For this purpose it will be assumed first that the subscriber at sub-' station SS2, Figs. 2 and 1, whose line terminates in exchange B, desires to converse with the subscriber at substation SS4, Fig. 1, whose line terminates in exchange C.

As before described, the subscriber at substation SS2, in order to complete the connection removes his receiver and dials the local listed number of the subscriber at substation SS4, exchange C, preceded -by the digit 9, assigned to exchange B.

When the receiver (not shown) is removed at substation SS2, the line switch LS2 is caused to operate in the usual manner in search of an idle line. It will be assumed that the trunk line extending to the selector S3 is the first one found to be idle and is therefore seized. Under this condition, the selector S3 is separated for operation in the usual manner, and it responds to the exchange digit 9 by raising its wipers opposite the ninth level of bank contacts and searching for an idle trunk line extending to exchange C. Assuming that the trunk line comprising conductors 26l, 262, and 263, and extending to exchange C by way of the impulse repeater IE3 and trunk line TL2, is the first one found to be idle, this trunk line is seized and connection to conductors 26l, 262, and 263 is made in the usual manner.

As is well known, a standard automatic selector is arranged to place a ground potential momentarily upon the test wiper thereof upon seizing an idle trunk line. This ground potential is extended over the release-trunk conductor or test conductor 262 to the impulse repeater 1R3, closing a circuit through the upper armatures of relays 2l8 and 220, by way of conductor 264, and through contacts of supervision-control relay 2l2 to the upper winding of shunt-control relay 2l3. Relay 2|3 is provided for the purpose of controlling the shunt connections around the associated repeating-coil windings. In order to prevent delay slightly the operation of relay M3, the second winding of the relay is normally closed through the inner-lower contacts of the relay,

the calling subscribers line when the impulse 5 repeater is seized. At its inner armature, line relay 203 closes a circuit for the slow-acting release relay 204. Relay 204 operates and places ground potential at its upper armature on the release trunk conductor 262 so as to maintain the connection established through the selector S3 and the line switch LS2, and to maintain the shunt-control relay 2l3'in operated condition. At its lower armature, release relay 204 opens a point in the circuit of the incoming answeringsupervisory relay 2| 0, and at its inner upper armature it closes a circuit through armature 243 of the selector-seizing relay for cut-through relay 205.

Cut-through relay 205 now operates and extends the incoming talking conductors 26i and 263 through to the left-hand repeating coil windings; at its inner upper armature it disconnects the armature of the impulse-receiving relay 226 from the selector-seizing relay 208 and transfers ltto the outgoing answering-supervisory relay 202; it prepares a circuit at its inner lower armature for the outgoing series relay M8; and at its lower armature it closes a circuit by way of the inner upper armature and resting contact of pulse-timer relay 2|! and conductor 206 for the Preparing relay 2, so as to start into operation the relay devices necessary to transmit a seizing impulse over the trunk line TL2 to cause the distant impulse repeater IRA, Fig. 1, to be prepared for incoming operation.

Transmitting the seizing impulse Upon operating, preparing relay 2 disconnects the talking conductors outgoing to the trunk line TL2 from the associated repeating-coil windings and extends them through the upper and lower windings of the retard coil 2l5 to the armatures of the dial-out relay 2l6; it grounds the free terminals of the filter condensers 256 and 259; and at its lower armature it grounds conductor 261, thereby closing a circuit through contacts, of the pulse timer relay 2|! and over conductor 260 for the dial-out relay 2H5. Relay 2|6 thereupon operates and closes the associated 60-cycle leads through the windings of the retard coil 2| 5 to the talking conductors of the trunk line TL2. This operation, it is to be understood, is for the purpose of transmitting a 60-cycle impulse to the distant repeater 1R4, Fig. l, to prepare it for incoming operation in a manner which will be described subsequently in connection with the repeater 1R3.

The dial-out relay 2l6 also extends the now grounded conductor 268 by way of conductor 209 and contacts of the outgoing series relay 2l8 to the winding of the pulse-timer relay 211. Relay 2, being provided with a copper collar on the armature end of its core, as indicated by the solid-black upper portion of the relay, is slow to operate so as to allow time for the impulse to be transmitted over the trunk line TLZ.

At the end of a slight interval, pulse-timer relay 2I'l operates and closes a locking circuit for itself at its inner armature to ground through the lower armature of the operated cut-through relay 205, at the same time opening the circuit of the preparing relay 2! and opening its own initial circuit. Relay 2 also opens the circuits of dial-out relay 2l6 at its lower armature. As a result, relays 2| I and 216 now restore and the 60-cycle seizing impulse transmitted over the trunk line TL2 is now terminated.

Dialling the number of the desired line The subscriber at substation SS2, having dialled the digit 9, assigned to exchange C, with results as described, now dials the first digit in the number locally assigned in exchange C to the line of the desired substation SS4, Fig. 1. When this digit is dialled,'each interruption produced in the calling line by the usual calling device (not shown) results in a momentary deenergization of line relay 203. Each time it deenergizes, line relay 2|3 momentarily opens the holding circuit of the slow-acting release relay 204 and it closes a circuit through contacts of the operated outthrough relay 205 for the slow-releasing outgoing series relay 2l8. As a result, relay 2| 8 immediately operates and remains operated throughout the series of impulses, because of its slow releasing characteristics. Upon operating, relay 2| 8 disconnects the incoming release trunk conductor 262 from the winding of shunt-control relay 2l3 and connects it to ground at an additional point,

associated with the left-hand repeating coil windings is, in effect, bridged directly across themcoming talking conductors in series with the resistor 210, which condition has been found to be very satisfactory in assisting the line relay 203 in following the dial control exercised over calling lines of various characteristics.

Outgoing series relay 2i8, at its inner upper armature, opens a point in the circuit of the incoming series relay'220 so as to prevent operation of relay 220 at this time. At the same time, relay 2l8 places a ground potential on conductor 206, so as to bring about an operation of the impulse preparing relay 2 M for the duration of the series of impulses. become operated and locked as described, the operation of preparing relay 2 does not affect the dial-out relay 2|6 at this time.

With the outgoing series relay 2! operated, each momentary deenergization of line relay 203 results in the closure of a circuit at the lower armature of the line relay and through the inner lower armature of relay 2l8 for the two-way repeating relay 2l2. Relay 2| 2 therefore responds momentarily to each of the impulses in the series.

Impulse correction The over-all result of the operations now to be described is that for each operation of the repeating relay 2l2 a corrected impulse is delivered under the control of the relays at retard coils 22l-225 to the dial-out relay 2l6.

. erably a sixty per cent break period, with a forty per cent make period between successive break periods).

Under the conditions assumed, the operation is as follows: when repeating relay 2!!! operates, it locks itself at its lower armature through contacts of the pulse-lock relay 221, and it closes a circuit at its inner upper armature through the retard coil 222 for the lower winding of the pulse Since impulse timer relay 2| I has timer relay 223. The operation of pulse timer relay 223 is delayed in two ways; (1) the building up of current through the lower winding of relay 223 is delayed by the inclusion of the retard coil 322 in its circuit, and (2) the upper winding of relay 223 is included in a closed circuit through contacts of the relay, having therefore a retarding efiect upon the building up of the flux the relay operates about four-tenths of an impulse cycle aiter its circuit is closed, which is two-tenths of an impulse cycle (under the assumed condition) before the repeating relay Elli restores responsive to the opening of its circuit by line relay when the latter relay reoperates. Moreover, the time of operation of pulse-timer relay 223 is six-tenths of an impulse cycle before the next reoperate time of the repeating relay 2E9.

When the pulse timer relay operates, it closes a circuit at its lower armature through the inner lower armature of the unoperated incoming series relay and over conductor 268 for the dial-out relay 2&8. Relay 2th thereupon operates and starts the first repeated dial impulse over the trunk line Th2 "from the GQ-eycle supply through the retard coil 2i?) and contacts of the operated preparing relay 2 it.

At its upper armature, relay 223 closes a cirsuit for the p 11 e-loelr relay 22 i, whereupon relay 22! operates and prepares a locking circuit for itself at its upper armature, while at its inner lower armature it closes a circuit for the pulsetirner relay 225 through the retard coil 226, at the same time unlocking the repeating relay 2li so as to permit this relay to restore now as soon as the dial impulse being delivered to it is termihated.

The pulse-timer relay 225 has delay provisions similar to those set forth in connection with the pulse timer relay 223 and it has a similar adjust ment as regards its operating time. Relay 225 therefore does not operate immediately.

At its lower armature, the pulse lock relay 22i closes a parallel circuit for dial-out relay 2H5 through contacts of relay 220, so as to maintain relay 2l6 operated over conductor 268 after the pulse timer relay 223 has restored.

When the repeating relay 2|9 restores (sixtenths of an impulse cycle after it operated, under the asumed conditions) upon the reoperation of line relay 293, it opens the circuit of pulsetimer relay 222 and closes a. lockingcircuit for pulse-lock relay 22! through the middle upper armature of pulse-timer relay 225 and the inner upper armature of the operated pulse-lock relay 22L As a result, the pulse-timer relay 223 immediately restores (two-tenths of an impulse cycle after it operated) and opens the initial circuit of the pulse lock relay 22! as well as the initial circuit of the dial-out relay 2 l6. Relay 22! does not restore, however, for the time being because of the before-mentioned locking circuit, and dial-out relay 2l6 remains operated throughthe lower contacts of relay 22 I.

At the beginning of the second impulse cycle, two things occur simultaneously; (1) repeating relay 2|9 reoperates responsive to the second deenergization of line relay 203, and (2) pulsetimer relay 225 operates because four-tenths of an impulse cycle have elapsed since its circuit was closed by the pulse-lock relay 22i responsive to the operation of the pulse-timer relay 223. The locking circuit of the pulse-lock relay MI is therefore opened at two points, and relay 22i restores as a result and opens the circuit of dialout relay M6 at its lower armature, at the same time opening the circuit of pulse-timer relay 225 at its inner lower armature and reestablishing the locking circuit of ,the now reoperated repeating relay H9.

The dial-out relay 2l6 having been operated aoaaear under the control of the impulse corrector for a period of time corresponding to six-tenths of.

anormal impulse cycle, now restores to terminate the first GO-cycle dialling impulse transmitted over the trunk line 'I'L2.

With the repeating relay 2E9 operations described before are repeated.

When the final impulse of the series has been transmitted, repeating relay 26%: does not reoperate, but the restoration of the pulse lock relay 22i and the described termination of the impulse takes place when the pulse timer relay 225 operates, which takes place at the same time that the reoperation of relay 2i?) would have taken place had the series contained another impulse.

Correcting short impulses at normal frequency Assume now that the calling device at the calling substation is operating at the normal speed and. therefore generating impulses at the normal speed and ratio, but that the characteristics of the calling line are such that line relay 283 does not restore quickly enough responsive to an interruption in its circuit. Under this condition the impulses delivered to repeating relay 2i9 are shorter than normal, although the time measured from the beginning of one impulse to the beginning of the next is the time of the normal impulse cycle. The operation of the impulse corrector in this case is as described before, except that repeating relay 2? does not restore immediately upon the quicker reoperation of line relay 263, but remains operated until its locking circuit is opened upon the operation of the impulselock relay 22 i which operation occurs at the same time that the initial circuit of relay 2 l9 normally is opened.

Correcting long impulses at normal frequency It will now be assumed for the moment that the line of substation SS2, although equipped with a calling device properly adjusted to operate at the normal speed, has characteristics which cause line relay 203 to delay abnormally long in reoperating after it has restored responsive to an interruption in the line circuit. Under this condition, each of the impulses delivered to repeating relay 2i9 is longer than normal. The impulse corrector in this case operates as previously described, as the repeating relay 2l9 merely remains operated for a very slight interval over its initial circuit after its locking circuit is opened upon the operation of pulse lock relay 22L Correcting impulses from a fast calling device Although calling devices are intended to be adjusted so that they deliver impulses at a rate of ten a second, the operating speeds normally tolerated in practice range from eight impulses a second to twelve impulses a second. For the purpose of explaining more fully the features of the impulse corrector of Fig. 2 it will now be assumed that the calling device at substation SS2 is slightly out of adjustment so that it sends impulses at a rate of twelve 21. second instead of ten 2. second. Under this condition, the reoperation of repeating relay 2 I9 occurs sooner pursuant to the second impulse than when the impulses are received at the rate of ten 9. second. Under this condition, the pulse timer relay 225 has not operated when relay 2l9 reoperates at the beginning of the second impulse received from the calling line. Nevertheless the pulse locking relay 22! is released when its locking circuit is opened upon reopera-ted, the

the reoperation of relay 2H), and the correspondingly shorter repeated impulse is terminated when relay 22! restores.

Correcting impulses from a slow calling device In order to explain the operation of the imtimer relay 225 operates following the closure of its circuit by the pulse-lock relay 22!, under the control of the pulse-timer relay 223. The termination of the first repeated impulse therefore is eifected (six-tenths of a normal impulse cycle after it began) under the control of relay 225, as relay 225 opens the locking circuit of the pulselock relay 22l and restores relay 22!, in spite of the fact that relay 219 has not yet operated.

In summation of the operations of the impulse corrector just described, it may be pointed out that the pulse-timer relay 225 is adjusted so as to permit the repeated impulses to be of maximum length when the calling device is operating more slowly than normal, while the termination of the repeated impulse is brought about by the reoperation of the repeating relay pursuant to the next received impulse when the calling device is operating at the maximum allowable speed, it being kept in mind that the starting of the repeated impulse is delayed for a predetermined time (usually four-tenths of a normal im pulse cycle) after the repeating relay has operated responsive to the incoming impulse. It is to be understood, however, that the timing described for the corrector is given by way of example only.

As is apparent the dial-out relay 2I6 responds to each repeated impulse and applies GO-cycle current to the conductors of the trunk line TL2 each time it responds, for the purpose of controlling the switchingoperation in the distant exchange C in a manner to be subsequently made clear. The resistor connected in circuit adjacent relay 2I5 is introduced for the purpose of improving the operation of the dial-out relay.

It may be pointed out that the condensers 256 and 257 operate in conjunction with the retard coil 2l5 to act as a filter to suppress undesirable harmonic frequencies, commonly present in commercial 60-cycle current.

When the series of impulses is terminated, repeating relay 2| 9 does not reoperate, and the final repeated impulse is terminated upon the previously described operation of the pulse-timer relay 225. At the end of the series of impulses, the outgoing series relay 2 l8 restores, permitting the shunt-control relay 213 to become reoperated from the grounded release trunk conductor 262 over its previously traced circuit, including conductor 264. The preparing relay 2| 4 restores when its circuit over conductor 266 is opened at the inner upper armature of the outgoing series relay 2| 8.

The previously described operations are repeated for each subsequent series of impulses corresponding to a digit in the desired number.

Answering supervision When the number has been completely dialled, and while the calling subscriber is awaiting a response, relays 203, 204, 205, 2l3, and 2|! are in operated position because of operations described heretofore, while the remaining relays of the impulse repeater 1R3 are in normal condition. With the repeater in this condition, an impulse of 60-cycle current is received over the trunk line TL2 from the called exchange when the called subscriber responds. This impulse of current is sent back from the impulse repeater 1R4, Fig. 1, in exchange C, in a manner which will be subsequently explained in connection with a call in the reverse direction over the trunk line TL2.

When the answering-supervision impulse is received over the trunk line TL2 from the distant exchange, the impulse receiving relay 226 responds. This relay is shunted around the talking condenser associated with the right-hand repeating coil windings, in series with condenser 212. The relay 226 is an alternating-current relay having a partially split core with one sectlon shaded or retarded, as indicated in the drawings. Accordingly, the relay does not vibrate in unison with the alternating current, but it operates and remains operated throughout an entire impulse of several cycles.

Upon operating at this time, impulse receiving relay 226 closes a circuit through contacts of the selector-seizing relay 208 and the inner upper armature of the operated cut-through relay 205 for answering-supervisory relay 202. Relay 202 is a "two-step relay, so designed and adjusted that an energization of its upper winding alone results in its operation through its first step only,

in which condition only its locking. contact is operated. This locking contact is identified by the letter X in the drawings, as is also the case with the various other two-step relays shown throughout Figs. 2, 3, and 4.

Upon operating through its first step only, the two-step answering-supervisory relay 202 closes a locking circuit for itself at its inner lower armature (the locking contact) through the lower armature of relay 20l to the grounded releasetrunk conductor 262. No current flows through the lower winding of relay 202 for the time being, because the initial circuit of the upper winding of the relay is still established at the contacts of the impulse receiving relay 226.

When the answering supervisory pulse is terminated, impulse receiving relay 226 restores and opens the initial circuit of the upper winding of relay 202, whereupon the relay becomes fully energized through the two windings in series and operates completely. At its lower armature, relay 202 prepares a locking circuit for the disconnectsupervisory relay 20l at its upper armature it transfers the supervisory-control circuit from its own upper winding to the winding of the disconnect-supervisory relay 20! and at its inner upper and middle upper armatures it reverses the connections between the windings of line relay 203 and the incoming talking conductors 26! and 263, thereby bringing about a reversal of ourrent-flow in the conductors of the calling line. This reversal of current-flow is used for the purpose of giving answering supervision in case the calling line is a line extending from an operators switchboard, and it is used to operate a meter or call register either in the exchange or on the subscriber's premises in case the calling line is a measured service line.

Th circuits of the impulse repeater 1R3 remain in the present condition throughout conversation.

the two subscribers replace their receivers. As-

suming that the receiver is first replaced at the distant substation, a disconnect-supervisory signal is received over the trunk line TL2 from the distant exchange being transmitted therefrom in a manner to be brought out hereinafter. When this disconnect supervisory signal is received be: ing an impulse of SO-cycle alternating current), impulse-receiving relay 225 responds and operates the disconnect supervisory relay 201! through its first step, the circuit including the upper armature of the operated answering-supervisory'relay 252. Upon operating through its upper wind ing, the disconnect-supervisory relay 2M 15' magnetized only to an extent that permits the op eration of its lightly adjusted locking armature (the inner lower armature). The operation of th inner lower armature of relay 20l results in the closure of the locking circuit from grounded release conductor 252 through the lower armature of the operating answering-supervisory relay 202.

When the impulse receiving relay 226 now restores, the locking circuit becomes effective and the two windings of relay 20l are energized in series, strengthening the magnetic field sufiiciently to bring about a complete operation of the relay. Upon completely operating, relay 20E opens the circuit of answering-supervisory relay 222 at its lower armature, whereupon supervisory relay 2G2 releases and restores the current flow in the calling line to its normal direction by reversing the connections between line relay 203 and incoming talking conductors '26l and 263 to normal.

This operation is used to give disconnect supervision in case the call is from an operator's switchboard and it may also be of utility in many other situations, as is well known.

Releasing the established connection When the receiver is replaced at the calling substation SS2, line relay 203 is permitted to fall back, whereupon an impulse is transmitted over the trunk line TL2 in the manner described hereinbefore and under the control of repeating relay 210 and relays 22!, 223, and 225. At this time, however, repeating relay 2|9 is not immediately restored, as in a case when a dialled impulse is being transmitted, as the line relay 203 does not reoperate after the receiver has been replaced. Therefore, relay 2I9 remains operated and maintains the pulse timer relay 223 operated to hold the dial-out relay 2l6 in operated position to I transmit a prolonged releasing impuse over the trunk line. It will be kept in mind, of course, that the outgoing series relay 2I8 is operated at this time and is maintaining the preparing relay operated at its inner upper armature.

At the end of the interval for which it is adjusted, release relay 204 restores, as its circuit is not again closed by line relay 203. Upon restoring, relay 204 removes ground potential at one point from release-trunk conductor 252, but conductor 262 is maintained grounded for the time being at the upper armature of the outgoing series relay 2l8. At its inner upper armature, release relay 204 also opens the circuit of cutthrough relay 205, permitting slow-acting cutthrough relay 205 to restore after a slight interval. Upon restoring, cut-through relay 205 opens the circuit of the outgoing series relay 210 at its inner lower armature and opens the locking cirand permits impulse timer relay 223 to restoreand open the circuit of the dial-out relay 215. Relays 2M and M6 are therefore restored to terminate the prolonged release impulse being transmitted to the distant end of the trunk line At its upper armature, outgoing series relay 2H3 finally removes ground potential from the release trunk conductor 262 so as to permit the lineswitch LS2 and the selector LS3 to release and clear out and to tree the repeater IRB for further use.

The release of the connection set up through the repeater ERG, Fig. l, in the distant exchange B takes place responsive to the release impulse in a manner which will become clear upon a further perusal of the specification.

Call from exchange C to exchange B In order to explain the remaining portions of the impulse repeater 1R3, Fig. 2, and to explain the way in which this impulse repeater operates in connection with a call in the reverse direction, it will now be assumed that the subscriber at substation SS5, Fig. 1, desires to obtain connection with a subscriber, at substation SS2, for example, in exchange B. Assume that the line switch LS4, Fig. 1, seizes the selector S8 when the receiver is removed at substation SS4, and that'the selector S6 seizes the trunk line TL2 by way of the impulse repeater 1R4 when the digit 0 is dialled. Under this condition, the repeater 1R4 operates as previously described for the impulse repeater IR3, Fig. 2, to transmit a seizing impulse over the trunk line TL2.

Seizing the incoming selector At this time, this impulse is received at the repeater ITS, Figs. 1 and 2, from the impulse repeater 1R4, Fig. 1. Impulsing receiving relay 226, Fig. 2, responds to the receiving impulse and closes a circuit through contacts of relays 208 and 205 for the lower winding of the two-step selecd tor-seizing relay 208. Responsive to the closure of the circuit through its lower winding, relay 208 is energized only sufliciently to operate its lightly adjusted inner upper armature to close the locking circuit.

It is to be noted thatincoming-release relay 201 is normally connected in parallel with the lower winding of relay 200, by way of armature; 245. Incoming-release relay 201, having a slaw-operating characteristic, is not operated at t. is time, as the seizing impulse is short, relative to the releasing impulse.

When the seizing impulse is terminated and the impulse receiving relay 226 restores, the looking circuit for relay 208 becomes effective and current flows through the two windings of the relay in series. As a result, relay 208 now operates fully. Upon operating fully, relay 208 grounds the release trunk conductor 262 at its upper armature by way of the upper armature of busy relay 205, thereby guarding the trunk line TL2 and the repeater IRS against seizure in exchange B, and bringing about the operation of shunt-control relay 213. At armature 2H and its middle lower armature, relay 208 connects the talking conductors extending to the left from the left-hand repeating coil windings to the talking conductors 281 and 282 extending to the incoming selector S5, Fig. 1, while at its lower armature it completes a control across the talking conductors 281 and 282 from the upper talking conductor through the upper left-hand repeating coil winding, conductor 213, contacts of relays 223 and 221 of the impulse corrector, lower armature of relay 208, resistance element 211, upper winding of the electro-polarized supervision-control relay 212, and through the lower left-hand repeating. coil winding to the lower talking conductor.

The line relay (not shown) of selector S5 is operated over the bridge circuit above traced to prepare the selector for its usual operation, but the electro-polarized supervision control relay 212 is not operated at this time, as it is designed and adjusted so as to operate only in case the current is flowing through both windings in the same direction.

As a further result of its complete operation, selector seizing relay 208 places a ground potential on conductor 215 at its inner lower armature thereby preparing a locking circuit for relays 208, 210, and 211 and closing a circuit through resistance element 210 for the polarizing winding of the electro-polarized relay 212. It disconnects the junction of its own winding from incoming-release relay 201 at armature 245; at armature 244 it connects up the common timing impulse conductor 216 for a purpose to be explained subsequently; and at armature 242 it transfers the control lead coming from the contacts of the impulse receiving relay 226 from the junction of its own upper winding to the two-way repeating relay 219, preparatory to operating relay 218 and the associated impulse corrector to transmit impulses to the seized selector S5, connected to the conductors 281 and 282.

Repeating the incoming dial impulses tarily responsive to each of the received impulses of the series. Each time it operates, impulse receiving relay 228 closes a circuit through the operated armature 242 of relay 208 for the repeating relay 219. Each time it operates, relay 219 closes a circuit for the incoming series relay 220, as

the outgoing series relay 218 is not operated at this time. By the combined action of repeating relay 219 and the pulse timer relay 225 incoming series relay 220 is operated and maintained operated throughout each incoming series of impulses.

Upon operating, incoming series relay 220 disconnects the lower armatures of pulse lock relay- 221 and pulse timer relay 223 from conductor 268 leading to the dial-out relay 218, and it prepares a circuit for operating the incoming release relay 201, which circuit is effective to operate the relay only when the established connection is to be released responsive to a prolonged releasing impulse.

Relays 219, 221, 223, and 225 cooperate in the manner hereinbefore explained to secure the repeating of corrected impulses. .The impulse repeating is performed by pulse timer relay 223 in conjunction with pulse lock relay 221, as in the described example of a call from exchange A to 5 exchange B. In the present example, the impulses delivered constitute breaks in the loop circuit extending to the seized selector S5, and are delivered at the upper contacts of relays 221 and 223 instead of at the lower contacts of these relays. As before, each impulse is repeated upon the operation of relay 223 and is terminated either by relay 221 or by relay 223, whichever one restores last. I

When incoming series relay 220 operates, it breaks the established circuit of the shunt control relay 213 at its upper armature, permitting relay 213 to restore and shunt the upper left-hand winding of the associated repeating coil at its upper armature. At its lower armature, shunt control relay 213 by-passes the lower left-hand winding of the associated repeating coil, the upper winding of supervision control relay 212, and resistance element 211. With relay 213 deenergized, it is to be noted that the control bridge across the talking conductors includes the resting contact and upper armature of relay 213, conductor 213, upper contacts of the impulse-corrector relays 223 and 221, lower armature of selector-seizing relay 208, and the resting contact and lower armature of relay 213. The impulsing bridge is shunted by a circuit which includes the lower left-hand repeating coil winding, associated talking condenser, and the resistance element 210, giving a control condition over the line relay (not shown) of the selector S5 which has been found by experiment to be very good.

At the end of the series of impulses, incoming series relay 228 restores and again connects up shunt control relay 213 to permit the latter relay to reoperate and place the circuits associated with the repeating coil windings in talking condition.

The selector S5 is operated responsive to the first repeated series of impulses, and it selects an idle connector in the desired group, the connector C4, Fig. 1, for example.

Under the assumed condition, the connector C4 is operated in the usual manner responsive to the two series of repeated impulses corresponding to the two final digits in the called number to extend connection to the line of the desired substation SS2.

Answering supervision When the called subscriber responds, the connector C4, Fig. 1, operates in the well known manner to reverse the current flow in its incoming talking conductors. The holding circuit for the line relay (not shown) of the connector C4 60 includes the upper winding of the electro-polarized supervision-control relay 212, Fig. 2. As a result, when the current flow is reversed, the two windings of relay 212 are energized in the same direction, and the operation of the relay is thus 65 secured.

Upon operating, relay 212 places a shunt around the resistor 214 so as to increase the current flow through its lower winding momentarily to maintain the relay operated for the time being irre- 70 spective of the direction of current flow in the upper winding. At the same time, relay 212 breaks the circuit of the shunt control relay 213 at its upper armature, momentarily deenergizing the shunt-control relay to shunt out the control wind- 75 ing (the upper winding) of the supervision control relay 2|2, leaving relay 2|2 entirely under the control of its lower winding.

At the lower armature, relay 2 |2 begins a series of operations which result in the transmission of an answering-supervisory impulse back to the calling exchange C. This is effected in a manner which will now be described.

With relay 2|2 operated, groundpotential on the grounded conductor 215 is extended at the lower armature of relay 2|2, through armature 255 and its resting contact, the lower armature of cut-through relay 205, inner upper armature and resting contact of pulse-timer relay 2|1, and thence by way of conductor 266 to the preparing relay 2. Preparing relay 2 is operated to prepare the circuit for the transmission of an alternating current impulse over the trunk line TL2. At its lower armature, relay 2|4 closes a circuit over conductor 261, through contacts of relay 2|1, and thence by way of conductor 268 to the dial-out relay 2|6. Relay 2|6 is operated to start the alternating-current impulse, and at its lower armature it closes a branch circuit over conductor 269 and contacts of the outgoing-series relay 2|8 for the pulse timer relay 2|1.

After the interval for which it is adjusted, relay 2|1 operates and. closes a locking circuit for itself at its inner upper armature, at the same time breaking the energizing circuit of relay 2 M. It also disconnects relay 2 6 at its lower armature, with the result that relays 2H and 2 l6 restore to terminate the answering supervisory impulse.

As a further result of its operation, relay 2|1 closes a circuit at its upper armature which extends ground potential from the serially related lower armatures of the line and release relays 203 and 204, by way of conductor 265 and the inner lower armature and resting contact of the disconnect-supervisory relay 2| I, to operate the answering-supervisory relay 2 I 0.

When relay 2|0 operates, it locks itself at its inner lower armature to the grounded conductor 215; it opens the shunt circuit around the resistance element 214 at armature 25|; it reoperates shunt-control relay 2|3 at its upper armature to place the circuit in talking condition; it prepares a locking circuit at armature 252 for the disconnect supervisory relay 2 and at armature 255 it opens the locking circuit of pulse timer relay 2 H, permitting relay 2 H to restore. Relay 2 does not reoperate now because its circuit is open at armature 255.

As a result of the described operations the answering supervisory impulse has been transmitted back over the trunk line TL2 to the calling exchange to bring about in the repeater, Fig. 1, operations described previously in connection with the repeater 1R2, Figs. 1 and 2, in the case of a call in the opposite direction over the trunk line TL2.

It is to be noted that relay 2|2 is temporarily rendered non-responsive in the manner described, while the answering supervisory impulse is retransmitted back over the trunk line. This is for the purpose of rendering the operation more reliable and to insure the completion of the signal in the event that the switchhook is not permitted to operate in normal manner upon its removal and to insure correct signal transmission in the event that the switchbook is subsequently moved up and down rapidly.

The circuits in the repeater 1R3 remain in this condition during conversation, relays 208, 2|0, 2|2, and 2 l3 being held operated.

Disconnect supervision Assume now that the conversation has been terminated and that the called subscriber at substation SSZ, Fig. l, is the first to replace his receiver. When the receiver is replaced, the connector C4, Fig. 1, operates in the usual manner to reverse the current flow in its incoming talking conductors back to normal direction, whereupon the current flow in the control winding of electropolarized supervision-control relay 2 I2, Fig. 2, is again reversed so that the two windings again oppose one another. Under this condition, relay 2|2 restores. Upon restoring, relay 2|2 closes a circuit at its lower armature from the grounded conductor 215 and through the lower armature of the answering-supervisory relay 2H) for the winding of disconnect supervisory relay 2| Upon operating, relay 2| closes a locking circuit for itself at its middle lower armature to conductor 215, by way of the operated armature 252 0 of relay 2|0, whereby it is maintained operated for the time being independent of further action of supervision-control relay 2|2.

At its lower armature, relay 2| extends ground potential from its own locked winding to the winding of the preparing relay 2|4. Relay 2 is again operated to prepare for transmitting an alternating-current disconnect-supervisory impulse over the trunk line TL2. At its lower armature it again closes the circuit over conductors 261 and 268, through contacts of pulse-timer relay 2|1 for dial-out relay 2|5. Relay 2|5 now operates and transmits the supervisory impulse over the trunk line TL2, at the same time closing a circuit over conductor 269 for pulse-timer relay 2|1.

When relay 2|1 operates, after the period for which it is adjusted, and breaks its initial circuit it does not lock itself because its locking circuit is open at armature 255 of relay 2) and at the lower armature of relay 2|2. Relay 2|1, being slow-releasing (as well as slow-operating), remains operated for a slight interval. At its upper armature relay 2|1 applies ground potential, obtained through the lower armatures of line and release relays 203 and 20l, by way of conductor 265 and the inner lower armatures of the operated relay 2|1 to the junction of the winding of relay 2H) and the associated current-supply resistor. Relay 2 0 is thereupon shunted and caused to restore. Upon restoring, relay 2||| disconnects its own winding at its inner lower armature from conductor 215, and at armature 252 it opens the. locking circuit of relay 2| in addition to opening the initial circuit of relay 2 at its lower armature. As a result, relays 2H and 2|4 now restore also. Slow acting relay 2|1 now finally restores.

At this point it may be mentioned that the supervision control relay 2|2 is again operated to bring about the results hereinbefore described in case the receiver is again removed or the hookswitch again raised at the called substation before the connection is released, as in the case of flashing the switchhook to signal the operator when the call has been extended through an operators switchboard. It will be observed,

therefore, that the operation of transmitting answering and disconnect supervisory signals may be repeated over and over as many times as relay 2|2 is operated and released.

Releasing the established connection When the subscriber at the calling substation SS4 replaces his receiver to release the established connection, the repeater 1R4, Fig. 1, in exchange C is caused to go through the operations described in connection with repeater 1T3, Figs. 1 and 2, to secure the release of the lineswitch LS4 and the selector S5, and to transmit a prolonged releasing impulse over the trunk line TL2 from exchange C to exchange B, Fig. 1. When this prolonged impulse is received, impulse receiving relay 226 remains operated for a much greater interval than when it is responding to setting impulses. When it responds at this time, it operates the two-way repeating relay 219 (through armature 224 of selector seizing relay 208 as before described), and relay 219 brings about the successive operation of relays 223, 221, and 225. Relay 225 closes a circuit for relay 201 at its lower armature through the lower armatures of the operated relays 221 and 220, relay 220 being operated at the upper armature of relay 219. Relay 201 because of the relatively great length of the releasing impulse has its circuit closed for a sufficient interval to bring about its operation. Relay 201 it will be noted is slow to operate because of its construction and does not therefore operate during the repeating of switch setting impulses because of its slow operating characteristic. Upon operating relay 201 extends its operating ground potential to the locking circuit of relay 298 and disconnects the locking circuit of relay 208 from the local supply of ground potential.

When the release impulse has been terminated, relay 226 restores and permits relays 219, 223, 221, and 225 to restore successively, and the incoming series relay 220 to restore after a short interval. The restoration of relay 225 results in the opening of the circuit of the incoming release relay 201. Since relay 201 is operated when its circuit is opened, the locking circuit of the selector-seizing relay 208 is also opened and also 208 restores immediately. Relay 201, being somewhat slow in restoring as Well as slow in operating, does not restore until a short time later.

Upon restoring, relay 208 removes ground potential from release-trunk conductor 262 at its upper armature so as to make the repeater 1T3 and the trunk line TL2 test idle again to selectors such as S3, and at armature 241 and 242 it disconnects the conductors 281 and 282 leading to the incoming selector S5, thereby bringing about the release of the connection set up by way of the selector S5. All of the circuit apparatus of the impulse repeater IE3 is in normal condition.

Forced release at the repeater 1R3 when the selector-seizing relay 208 is operated v responsive to a seizing impulse received at the impulse receiving relay 226 and causes the associated selectorS5 to be seized and prepared for opera-- tion, the common timer lead 2115 coming from the common impulse device 283 is connected at armature 244 through contacts of relays 210 and 209 to the upper winding of the two-step forcedin the partial energization of relay 209 through its upper winding. Only the lightly adjusted locking armature of relay 209 is operated at this time, and it closes a locking circuit for the two windings .in series from the grounded conductor 1., 215tby way of armature 252 and its resting con- When the impulse is terminated, relay 209 operates fully on account of its two windings being at that time energized in series. in

With relay 209 operated fully, the receipt of the next impulse (say thirty seconds to one minute later) results in the closure of a circuit through the operated upper armature of relay 209 for the incoming release relay 201 unless the answering -13 supervisory relay 210 has been operated in the meantime to restore relay 209. If relay 209 is still operated, relay 201 responds to the impulse and opens the initial locking circuit of relay 208, holding this relay operated in parallel with its own winding for the time being. Then, when the impulse is terminated, relay 208 restores and clears out the repeater as described. In the normal operation of the repeater, the call is put through to the desired line and is ordinarily an- 33 swered, or else the connection is released in the normal way if the called line is busy, before the forced released described has had time to be effective.

It is to be noted that the answering supervisory relay, which is operated as previously described when the called subscriber responds, opens the locking circuit of relay 209 at armature 252. so as to restore relay 209 and thereby prevent the forced release operation from being performed during conversation. It will be understood, however, that' the forced release operation may be again initiated in casethe regular releasing operation does not take place following the restoration of answering supervisory relay 5 210, as described, when the receiver is replaced at the called substation. This will be readily apparent, as relay 210, upon releasing, again prepares the locking circuit of relay 209 and again connects the relay to the common impulse lead 55 216.

Double seizure of an inter-exchange trunk line In order to explain an additional special provision it will be assumed that the trunk line TL2,

Figs. 1 and 2, is seized at about the same moment in exchanges C and B. When the repeater IE3 is seized in exchange B, the placing of ground potential on the release trunk conductor 262 by the seizing switch brings about the hereinbefore .65 described operation of shunt control relay 213 over conductor 264, accompanied by the described successive operation of the line, release, and cutthrough relays 203, 204, and 205. The operation of the cut-through relay 205, as hereinbeiore described, at its lower armature sets in motion the operation involving relays 214, 215, and 211 to cause a. seizing impulse to be transmitted to the distant exchange.

It will be understood that similar operations iii are taking place at the same time in the distant exchange, and the two seizing impulses are transmitted without avail if the trunk line seizure at the two ends is accomplished exactly at the same time, which happening is extremely rare. If one seizure, the seizure in exchange B, for instance, takes place slightly later, the cutthrough relay 205 is unable to operate responsive to the operation of, release relay 204, as the selector-seizing relay 215 has been operated responsive to the seizing impulse received from the distant end. In this case, busy relay 206 is operated through the actuated armature 243 of seizing relay 208. Upon operating, relay 206 disconnects the incoming relcase trunk conductor 262 from the upper armature of relay 208, leaving the incoming release trunk conductor 262 grounded only at the upper armature of release relay 204. Busy relay 206 also connects the associated common busy-tone lead through the usual small limiting condenser to the upper talking conductor, thereby transmitting busy-tone current to the calling substation to inform the subscriber thereat of the busycondition.

When the calling subscriber replaces his receiver under these conditions, the line and release relays 203 and 204 restore successively, and release relay 204 opens the circuit of the slow releasing busy relay 205. Release relay 204 also disconnects ground potential at its upper'armature from the incoming release trunk conductor 262 so as to permit the local switches involved in the connection to release. A moment later busy relay 206 restores and at its upper armature again places ground potential on release trunk conductor 262 through the actuated upper armature of selector-seizing relay 208, thereby guarding the trunk line against further seizure in exchange B.

Abandoned calls Special provisions have been made for clearing out the repeaters on the two ends of a trunk line when a call is abandoned before the connection is put through to the called line. It will be recalled that a releasing impulse is transmitted by the repeater 1R3 over the trunk line 'I'L2 when an outgoing connection through the repeater 1R3 of the trunk line TL2 is to be released. This impulse is transmitted throughout the time required for the slow releasing release, cut-through, and outgoing-series relays 204, 205, and 2|8, to restore successively, following the opening of the circuit of release relay 204 by line relay 203. It

will be recalled also that the circuit for preparing relay 2 is closed at this time at the inner upper armature of the outgoing series relay 2I8, operated through contacts of relays 203 and 205, and that the releasing impulse is transmitted through the contacts of dial-out relay 2l6, which is operated over conductor 258 from the impulse corrector and under the control of repeating relay 2l9. Repeating relay 2l8, it will be recalled, is operated through contacts of line relay 203 and outgoing series relay 2|8 to maintain pulse-timer relay 223 operated to hold the circuit of dial-out relay 2|6 closed until relay 2I8 restores.

In the example assumed and described hereinbefore, the releasing operations took place only after the call had been completed and conversation had taken place. It is evident that the releasing impulse will be transmitted from the repeater 1R3 over the trunk line 'I'L2 at any stage of the connection after the repeater m3 has been seized, as the relays 201-205 operate successively upon the seizure of the repeater and thereby make the necessary circuit preparations for the transmission of the releasing impulse.

A special condition which must be considered is the one arising when the calling subscriber abandons the call only a moment after a selector such as the selector S3 has been operated to extend a connection to the impulse repeater 1R3. At this time, the preparing and dial-out relays 2 l4 and H5 are operated to transmit a relatively short seizing impulse over the trunk line 'I'L2, the length of which is determined by the slow-operating characteristic of pulse-timer relay 2.

Now, in the event that the calling subscriber replaces his receiver and brings about the deenergization of line relay 203 while the seizing pulse is being transmitted, outgoing series relay 2" is operated by line relay 203 through contacts of relay 205 to close a new circuit for preparing relay 256 and to connect up repeating relay 2l9. Repeating relay 2i9 operates and brings about the operation of pulse-timer relay 223 to close a new circuit over conductor 268 to maintain dial-out relay operated. The circuit for the pulse timer relay 211 is opened at the lower contacts of outgoing series relay 2i8, whereby the operation of pulse timer relay 2|! is prevented at this time.

Relays 2M and 216 are now maintained energized to prolong the impulse of current being transmitted over the trunk line TL2 until relays 204, 205, and H8 restore.

When relay 2 l8 restores, relays 2 l4 and 2 I are permitted to fall back as hereinbefore described, finally terminating the impulse.

As will be pointed out subsequently, this prolonged impulse, instead of causing the distant repeater 1R4, Fig. 1, to seize the associated incoming selector, causes the said repeater ml to refrain from seizing the associated incoming selector and to become cleared out upon the termination of the impular.

Consider now the case when the trunk line TM is seized in exchange B by way of impulse repeater IE4 and the call is immediately abandoned. Under this condition, as was described above, the impulse received at the impulse repeater IR! is a prolonged releasing impulse in place of the somewhat shorter seizing impulse ordinarily received as the first impulse pursuant to the establishment of a connection.

Upon the receipt of this impulse, impulse receiving relay 226 responds and closes a circuit through contacts of relay 208, and through the inner upper armature and resting contact of cut-through relay 205, for the lower winding of the two-step selector-seizing relay 208. Relay 208 operates as before to close a lightly adjusted locking contact (the inner upper armature and associated contact). At the same time, a circuit extends in parallel with the lower winding of relay 208 through armature 245 and its resting contact for the incoming-release relay 201. Relay 201 is a slow acting relay, being adjusted so that it does not operate in parallel with the lower winding of relay 208 when a relatively short selector-seizing impulse is being received. In the present assumed example, however, the impulse being received is a prolonged releasing impulse and is of suflicient duration to bring about the operation of relay 201. Upon operating, the relay 20! removes the local ground connection from the inner upper armature of relay 208 and substitutes the ground potential now being applied by the armture oi the impulse-receiving relay 226. As a Cal result of this, when relay 226 restores, at the end of the prolonged impulse, there is no locking potential present to cause the upper winding of relay 208 to become energized in series with the lower winding of'the relay. Relay 208, therefore, does not operate fully but restores and opens its looking contacts. A moment later, relay 201 restores and leaves the impulse repeater IR3 in a completely cleared-out condition.

Compoaited-trunk-line operation without voice current repeaters The foregoing description of theoperation of the repeater 1R3, Figs. 1 and 2, has been given under the assumption that the trunk line TLZ does not include a physical circuit composited for telegraphic or similar operation over the conductors thereof. It has been determined by experimentation that a 60-cycle current is rather low in frequency for advantageous signalling over a circuit composited for telegraphic or similar signal operation, as there is likelihood of mutual interference between the dialling impulses and the telegraphic impulses. I For operation in-conjunction with composited lines, the leads extending down from the contacts of the dial-out relay 2|6 are connected to a. higher frequency source, 120- cycles for example. l-cycle current is recommended mainly because it may be obtained readily from the commercial GO-cycle current by using a well known form of frequency-doubling device. The impulse receiving arrangement is modified somewhat when 120-cycle signalling current is used. a

For the reception of 120-cycle signal impulses, the jumpers extending to relay 226 and its armature are removed and jumpers indicated by the dotted lines are connected up to the circuit of relay 22B and to the armature of relay 229. It may be pointed out that the retard coil 221 and the condenser 254, in series, form a tuned couple designed to peak at about 120-cycles, whereby a maximum potential is impressed on the terminals of polarized relay 228, relay 228 being in shunt of condenser 254. The armature of relay 228 normally stands in neutral position and is forced first in one direction and then in the other by the successive positive and negative surges of the 120-cycle current.

Each time the armature of relay 228 is moved in either direction, the circuit of relay 229 is closed. Relay 229 is shunted by a relatively high resistor, which arrangement makes the relay sufficiently slow to release that it remains operated throughouta series of vibrations of the armature of polarized relay 228, but relay 220 restores almost instantly when the armature of relay 228 comes to rest.

From the above explanation it will be seen that relay 228 responds to each received impulse of 120-cycle current by vibrating its armature, and that relay 220 operates for the duration of the impulse and then restores immediately. As a result, relay 228 operates to control the circuits in the impulse repeater 1R3 in the manner described in. connection with the armature of impulse receiving relay 226.

It may be pointed out that the variable re- :istcr 255, shunted across the polarized relay 228, may be adjusted from time to time in order to improve the response of relay 228 under, for example, varylng temperature or other conditions I which may affect the operation.-

Voice frequency diaZling--slow-relay signal control It has been previously pointed out that the trunk lines passing from exchange A-to exchange B, Fig. 1, pass through a voice-current-repeater station, there being a separate two-way voicecurrent repeater for each trunk line, and'that the practical limitations of a voice-current repeater require that the dial impulses be transmitted as impulses of current of a voice frequency and of an intensity of the same order as the intensity of the voice currents. It is necessary, therefore, to make special provisions to prevent impulses of voice currents arising during conversation from being interpreted as signallingimpulses, as will be pointed out in the course of the description.

Two modifications of the voice-frequency dialling arrangement have been provided, one being shown in Fig. 3, the other in Fig. 4. The principal difierence between Figs. 3 and 4 is that, in Fig. 3, slow-releasing relays have been provided to control signalling operations apart from the actual dialling impulses, while in Fig. 4 a tuned signal-receiving relay is provided to respond to the signal-frequency modulations of the thousand-cycle carrier current. I

The repeater IRI, as shown in Fig. 3, will now be described.

Three vacuum tubes are associated with the repeater IRI, a power amplifier 332, a screen-grid voltage amplifier 331, and a detector tube 338. Plate current and biasing potential for the tubes 336, 331, and 338 are furnished by the rectifier tube'335 and associated apparatus. The transformer 33!, it will be noted, has one winding for lighting the filament of the rectifier tube 335, another winding for furnishing the current to the rectifier for use by the vacuum tubes, and a third winding for heating the filaments of the heater-type tubes 336, 331, and 338. Choke coils 332 and 333, together with the associated bypass condensers, form the usual type of filter to smooth out the sipples in the rectified current.

The multi-tap resistor indicated generally by the reference character 334 provides nine volts posi tive potential over lead 346 for grid biasing purposes, 100-volt positive plate and screen-grid current over lead 341, one 115-volt current over lead 348 and 200-volt current over lead 349.

Each of the tubes 336, 331, and 338 is of the usual heater type; each includes the heater element, a cathode element, a control grid, and a plate. The voltage-amplifier tube 331 has in addition a screen grid interposed between the usual control grid and the plate element of the tube.

The transformer 36!, common to a group of impulse repeaters, furnishes 1000-cycle current for signalling and dialling purposes. The transformer 364, also common to a group of repeaters, furnishes GO-cycle current which is used, as will be subsequently described, for modulating the 1000-cycle current for the purpose of signalling apart from the transmission of switch-setting impulses.

The relays 32l, 322, and'232 are each provided with a resistor in shunt of its winding, the resistance of which is relatively high but low enough 7 the rate of sixty a second, but neither of the re- 

